User level control of power management policies

ABSTRACT

In one embodiment, the present invention includes a processor having a core and a power controller to control power management features of the processor. The power controller can receive an energy performance bias (EPB) value from the core and access a power-performance tuning table based on the value. Using information from the table, at least one setting of a power management feature can be updated. Other embodiments are described and claimed.

BACKGROUND

Advances in semiconductor processing and logic design have permitted anincrease in the amount of logic that may be present on integratedcircuit devices. As a result, computer system configurations haveevolved from a single or multiple integrated circuits in a system tomultiple hardware threads, multiple cores, multiple devices, and/orcomplete systems on individual integrated circuits. Additionally, as thedensity of integrated circuits has grown, the power requirements forcomputing systems (from embedded systems to servers) have alsoescalated. Furthermore, software inefficiencies, and its requirements ofhardware, have also caused an increase in computing device energyconsumption. In fact, some studies indicate that computing devicesconsume a sizeable percentage of the entire electricity supply for acountry, such as the United States of America. As a result, there is avital need for energy efficiency and conservation associated withintegrated circuits. These needs will increase as servers, desktopcomputers, notebooks, ultrabooks, tablets, mobile phones, processors,embedded systems, etc. become even more prevalent (from inclusion in thetypical computer, automobiles, and televisions to biotechnology).

In many computing environments, it is an established fact that for muchof the time, computing systems such as servers are operating well belowtheir peak performance level. During these periods of low utilizationthe focus is on saving as much power as possible in order to reduce theenergy costs. Power management technologies can deliver significantpower savings during periods of low utilization. However any powermanagement technology involves a power/performance tradeoff.

Due to increasing integration, many processors can include powermanagement technologies which can control up ⅔ rds of total platformpower. In many cases these technologies are controlled by a powercontrol unit (PCU) in the processor. Each power management feature isspecifically tuned in design to achieve an optimal power/performancetradeoff. At the time of tuning, there is little knowledge of the actualworkload and usage pattern for the system in the field. Given this lackof knowledge, the tuning process is conservative and is necessarilybiased towards losing as little performance as possible. This approachprevents significant power savings for an end user who is willing totolerate more performance loss in return for power savings.

Thus typically power management features are statically tuned totolerate very little performance loss. This results in several negativedownsides. First, at low utilizations where an end user can toleratehigh performance loss, available power savings are not realized. Second,an end user typically has no choice regarding power/performancetradeoffs, other than default profiles provided by an operating system(OS). Given the complexity involved in tuning power management features,end users rarely venture into tuning individual features for theirtarget usage, and thus the potential benefit of the features are oftennot realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an architecture of a tuning circuit for atunable power performance loadline technique in accordance with oneembodiment of the present invention.

FIG. 2 is a block diagram of a tuning table in accordance with anembodiment of the present invention.

FIG. 3 is a flow diagram of a method in accordance with an embodiment ofthe present invention.

FIG. 4 is a block diagram of a processor in accordance with anembodiment of the present invention.

FIG. 5 is a block diagram of a multi-domain processor in accordance withanother embodiment of the present invention.

FIG. 6 is a block diagram of a system in accordance with an embodimentof the present invention.

FIG. 7 is a block diagram of a multiprocessor system with apoint-to-point (PtP) interconnect in accordance with one embodiment ofthe present invention.

FIG. 8 is a block diagram of a partially connected quad processor systemin accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments provide a so-called energy performance bias (EPB) as anarchitectural feature. Control of this parameter allows for a simplehigh level input from an end user to indicate a power/performancetradeoff preference from the end user. This input can be used to providemultiple tuning levels with different points of power and performancetradeoff. By associating this energy performance bias with direct userinput, embodiments enable the end user to directly controlpower/performance tradeoff in a simple manner. As used herein the terms“end user” or “user” are comprehended to include computer users ofvarying degrees, including technical and non-technical users,information technology (IT) personnel, data center personnel and soforth.

Thus instead of providing complete tuning flexibility for each powermanagement technology and allowing an end user to tune each feature, asingle input can be provided by the user to control these differentfeatures. The EPB value may thus correspond to a single input value tocontrol a plurality of power management features. Furthermore,understand that the provision of the EPB value can be from a variety ofexternal entities including but not limited to an operating system (OS),a basic input/output system (BIOS), an external embedded controller of aplatform such as a baseboard management controller (BMC), a data centercentral management software and communicated via a network and a nodemanager device or so forth to a platform, among others, automatically orvia a user. And in some embodiments, the end user may be prevented fromsuch individual control. As such, the inherent difficulty in exposingall of a large number of power management features to the end user canbe avoided, particularly as most end users have little or no knowledgeas to how to tune such individual features. In practice, 90% of serverusers never change the default power management configuration for theserver, and a very similar dilemma exists in client usage models aswell.

Table 1 below shows a list of power management features available indifferent processor models and which can be controlled globally usingone or more EPB inputs in accordance with an embodiment of the presentinvention. It can be seen from Table 1 that the number features isdisparate and large. This list continues to grow with each generation ofprocessor. As seen, power management features can be performed within aprocessor itself, a memory or memory interconnect, or other interconnectstructures. Embodiments can provide for global control of a plurality ofpower management features of a processor including, in some embodiments,those shown in Table 1. However, understand that this listing isexemplary only, and other power management features can be controlledusing an EPB value in accordance with an embodiment of the presentinvention.

TABLE 1 Index Platform Area Processor 1 Processor 2 Processor 3 1 CPUTurbo Turbo Turbo 2 CPU C-State C-State C-State Demotion DemotionDemotion 3 Memory CKE CKE CKE 4 CPU QPI Los Not Supported QPI LOs 5 CPUNot Supported Turbo Turbo Demotion Demotion 6 CPU Not Supported C-StateC-State Undemotion Undemotion 7 CPU Not Supported Not Supported TurboUpside Control 8 CPU Not Supported Energy Not Supported Efficient Turbo9 Memory Not Supported Not Supported CKE Slow 10 Memory Not SupportedNot Supported Opportunistic Self Refresh 11 CPU Not Supported NotSupported QPI LOP 11 CPU/PCI Not Supported PCIE LOs PCIE LOs

A power/performance loadline is a well accepted representation of powerconsumption of a system at different utilizations. This loadlinerepresents the power consumed at each delivered performance level andtakes into account the performance impact of a power management feature.Via an energy performance bias setting in accordance with an embodimentof the present invention, tuning of a power performance loadline can berealized. This setting or slider thus allows an end user to choose arange of choices between performance-oriented tuning settings and powersaving-oriented tuning settings. Each EPB value can be mapped to acorresponding level of tradeoff between power and performance.

Although the following embodiments are described with reference toenergy conservation and energy efficiency in specific integratedcircuits, such as in computing platforms or processors, otherembodiments are applicable to other types of integrated circuits andlogic devices. Similar techniques and teachings of embodiments describedherein may be applied to other types of circuits or semiconductordevices that may also benefit from better energy efficiency and energyconservation. For example, the disclosed embodiments are not limited toany particular type of computer systems, and may be also used in otherdevices, such as handheld devices, systems on chip (SoCs), and embeddedapplications. Some examples of handheld devices include cellular phones,Internet protocol devices, digital cameras, personal digital assistants(PDAs), and handheld PCs. Embedded applications typically include amicrocontroller, a digital signal processor (DSP), network computers(NetPC), set-top boxes, network hubs, wide area network (WAN) switches,or any other system that can perform the functions and operations taughtbelow. Moreover, the apparatus', methods, and systems described hereinare not limited to physical computing devices, but may also relate tosoftware optimizations for energy conservation and efficiency. As willbecome readily apparent in the description below, the embodiments ofmethods, apparatus', and systems described herein (whether in referenceto hardware, firmware, software, or a combination thereof) are vital toa ‘green technology’ future, such as for power conservation and energyefficiency in products that encompass a large portion of the US economy.

Referring now to FIG. 1, shown is a block diagram of an architecture ofa tuning circuit for a tunable power performance loadline technique inaccordance with an embodiment of the present invention. In theembodiment of FIG. 1, each logical thread can provide an input, namelyan energy performance bias value, referred to herein as an EPB value.Note that this logical thread can correspond to a logical processor orother execution entity. The policy choice between performance and powercan be provided per logical thread via a register or other storage,e.g., a 4-bit input register. In this example, 16 levels of power andperformance tradeoff can be realized, in such an embodiment. Accordingto one convention, a value of zero represents a very low (or even zero)tolerance for performance loss while saving power. On the other hand avalue of 15 represents a high tolerance for performance loss and savingas much power as possible. Note that this EPB input can be provided byan operating system (OS) or by system basic input/output system (BIOS),or even by a user level application directly or indirectly.

In one usage model, where an operating system supports multiplepower/performance profiles, the OS configures the energy performancebias register to an appropriate value based the power/performanceprofile chosen by an administrator which is one example of an end user.To this end, embodiments may provide a user interface to request andreceive user selection of a given EPB value. This user interfacefunctionality can be accommodated within BIOS or an OS or other customsystem level software. In an advanced usage model, a data centeradministrator or other information technology personnel can provide theinput based on time of day policies. For example, during times of peakusage, the administrator can choose to configure a value of 0 whileduring non-peak hours the administrator can choose to configure theserver to a value of 15 to save as much power as possible.

In another usage model for advanced application level control thatsupports the option for application monitoring of the level ofperformance that the application expects to receive under a level ofservice agreement, the application may tune through an OS service thelevel of performance loss that is acceptable by the application underits current level of operation.

As seen in FIG. 1, a power management tuning circuit 100 can be used toreceive incoming EPB values from multiple cores of a multicore processorand use these values to determine an appropriate tradeoff between powerand performance policies and provide settings to the agents responsiblefor controlling various power management features of a system includingthe processor. In one embodiment, circuit 100 can be implemented inlogic of a power control unit (PCU) of a processor, although embodimentscan be implemented in other hardware or software. As seen, circuit 100includes a sampler 110 that can receive incoming EPB values from thevarious cores. Note that these values received can be from logicalthreads, in one embodiment, which provide a value based on itsprogramming. Although described in the embodiment of FIG. 1 as beingreceived from cores, in various embodiments, EPB values can be percore's thread, per core or per package that includes a number of cores,or other granularity. By these multiple inputs, thread specificoptimizations can be made based on a workload being executed. ReceivedEPB values can be stored in temporary storage, e.g., registers withinEPB sampler 110 at a sampling point, which may be according to a giveninterval. In one embodiment, the EPB inputs can be sampled at apredetermined interval, e.g., once every 1 millisecond (ms). The samplesobtained from the various cores can be provided to an EPB combiner 120that can generate a single value from these multiple values. For powermanagement optimizations that are not thread specific (for example, of amemory controller, interconnect, memory or so forth), a mechanism can beprovided to resolve the inputs from the multiple threads. In oneembodiment, this resolution can be via a policy of favoring performance.To this end, a min function can be performed on all thread's inputs andthe resulting value represents the most performance favoring EPB input.This value can then be used to determine the processor power/performancepolicy level. However, understand the scope of the present invention isnot limited in this way. As an example instead of a minimum function, anaveraging between the individual thread values can be performed. Anotherexample is to make the minimum function per control power domain thatmay hold several sets of cores or threads.

Still referring to FIG. 1, the single value corresponding to, e.g., theminimum value of the EPB value, can be provided to a bin generator 130.Note that in various embodiments this bin generator may be optional toprovide for finer-grained control. That is, bin generator 130 maygeneralize the tuning by taking the received EPB value and placing itinto one of multiple bins that correspond to multiple coarser-grainedlevels of control such that the EPB value thus determined can bebucketed into an internal value. As described above, with a 4-bit EPBvalue, 16 levels can be provided. However, some systems may not besufficiently complex with regard to the number of power managementfeatures, and thus the determined EPB value can be corresponded to oneof N bins less than 16 individual levels. In one embodiment, to simplifyand minimize the amount of tuning for a processor, the EPB value can beallocated to one of N buckets or bins. N can equal four, in oneembodiment. In this example, each bucket represents a continuous rangethat is ¼th of total power management range. These buckets may directlymap to power/performance profiles supported by certain operatingsystems. Table 2 shows the tuning criterion for four buckets inaccordance with one embodiment of the present invention. However,understand that different tuning criteria can be used in otherembodiments.

TABLE 2 Resolved EPB Input Range Power Profile Power Management FeatureTuning Target 0-3 Performance Tolerate up to 0.1% performance loss 4-7Balanced Tolerate up to 2% performance loss. Power Performance savingshould be at least 2x performance loss.  8-11 Balanced Tolerate up to 5%performance loss. Power Power saving should be at least 1x performanceloss. 12-15 Power Saver Tolerate >5% performance loss. Save as muchpower as possible.

Still referring to FIG. 1, the bin value thus determined can be providedto a change detector 140 that can determine whether the value of the binhas changed since the last analysis interval. If not, no furtheroperation of circuit 100 may be performed for that analysis interval. Ifinstead the value has changed, this new value can be used to access apower/performance table 150. In various embodiments, this table can bestored in a processor, e.g., in non-volatile storage of the PCU. Thetable can be pre-tuned to provide user transparent tuning settings thatcorrespond to a selected power/performance profile. In general, table150 can include one or more entries for each power management feature.Each entry can further include a plurality of fields, each associatedwith one of the buckets (or indicated EPB values) to store a parameterfor use in that feature or setting of a feature. These parameters may bevalues used for a certain power management feature, or can be an addressto code that is executed for a given setting.

Referring now to FIG. 2, shown is a block diagram of a tuning table inaccordance with an embodiment of the present invention. As shown in FIG.2, table 150 includes multiple entries 151 ₀-151 _(n). As seen, each ofthese entries can be associated with a given power management featuresetting. Some features may have more than one setting associated withthem. For other power management features, only an entry for a singlesetting is provided.

As further seen in table 150, each entry includes a plurality of fields.In the embodiment shown in FIG. 2, fields 152, 154, 156 and 158 areprovided. Each field is associated with a given one of the multiple binsas discussed above, namely a given policy. In other embodiments, eachfield can be associated with a given EPB value. Thus for each powermanagement feature setting, every bin can have a value in itscorresponding field. In specific implementations, each field may includea value that can be used to control enablement of a power managementfeature, provide a configuration register value or so forth. For somefeatures and settings, it is possible that multiple bins may have thesame value, however the scope of the present invention is not limited inthis aspect.

Based on the bin value, a respective column of the table can be accessedand all of the fields of the accessed column can be read out, e.g., as asingle vector read or iteratively via a field of an entry per cycle. Aswill be discussed below, these values output from the table can beprovided to a change detector 160. Although shown at this high level inthe embodiment of FIG. 3, understand the scope of the present inventionis not limited in this regard.

In some embodiments, in addition to the EPB input, a workloadconfiguration input can be provided. To this end, the table can have 3dimensions such that based on the workload configuration input, adifferent set of entries for the defined power management features canbe accessed, as different values may be present in the table fordifferent workload configurations. By this workload configuration inputa vertical user having an understanding and control of the exactworkloads running on their systems can benefit from well-tuned settings.As examples, a user can configure a workload input as non-uniform memoryarchitecture (NUMA), uniform memory architecture (UMA), input/output(I/O) intensive, etc. This input allows for choosing tuning settingsthat favor a specific workload pattern. For example, if the workload isNUMA, aggressive settings can be applied to off-chip interconnects suchas Intel® Quick Path Interconnect (QPI) links to save as much powerpossible while causing very little performance impact, as off-chipaccesses can be expected to be low. Thus for embodiments in which aworkload configuration input is provided, it can be used as anadditional input to access the table.

Once a new set of configurations is determined from access to the tuningtable, the target features can be updated. There are two classes ofconfigurations. For features like a power C-state auto demotion andturbo upside clipping, the configurations can be internal to powermanagement code, such as present in firmware of the PCU. In this casethe update can be effected by loading new values into an internalfeature specific data structure such as one or more configurationregisters. In a second class of configuration, the configuration valueis specific to an entity that resides outside the PCU. For example, aclock related configuration can be implemented in the memory controller.In this case, the PCU can initiate a series of writes to targetconfiguration space to update the settings. In order to minimize thenumber of writes, each configuration value can be compared to theprevious value and a write is issued only if the actual configurationvalue changes.

Accordingly, with further reference back to FIG. 1 the identified fieldof the multiple entries of table 150 can be output to a change detector160 to determine whether the values have changed from the previousoutput. Note that for certain power management features, settings maynot change when a bin changes level. Thus change detector 160 acts as afilter to filter from sending messages for updates when in fact noupdate is needed. If a change in fact has occurred, it may be sent fromchange detector 160 to the indicated destination. As described, manypower management features can be controlled using the PCU, andaccordingly updated settings can be sent to a PCU updater 170 which thusmay update the settings, e.g., by updating values in configurationregisters, other storages, enabling or disabling certain powermanagement features, changing variables used with regard to duration ofpower management features or so forth.

If instead the power management feature is for a non-PCU controlledfeature, update messages can be sent to the destination, e.g., via oneor more write messages including the information. Although shown withthis particular implementation in the embodiment of FIG. 1, understandthe scope of the present invention is not limited in this regard.

Referring now to FIG. 3, shown is a flow diagram of a method inaccordance with an embodiment of the present invention. As seen, method200 can be performed, e.g., using policy management logic of a PCU orother power controller. Method 200 begins by receiving an energyperformance bias value from multiple threads (block 210). As discussedabove, these threads can be logical threads or equivalently the EPBvalues can be received from the cores themselves. Next, a global EPBvalue can be determined from the received EPB values (block 220). Forexample, a min function can be performed or an average obtained fromthese multiple values. Then, this global EPB value can be placed into abin of multiple performance level bins (block 230). Such binningprovides a smoothing function, although it may not be present in someimplementations where very fine-grained control of power and performancetradeoffs is desired.

Still referring to FIG. 3, control next passes to diamond 240 where itcan be determined whether a bin change has occurred since the lastevaluation interval. If not, method 200 concludes for that givenevaluation interval which can be, e.g., on the order of approximately 1ms.

If instead a bin change has occurred, control passes to block 250 wherea power-performance table can be accessed based on the bin. This tableaccess thus can be used to read out for the given bin, and for each ofmultiple power management features, one or more settings or other valuesused to control the power management feature. This reading and theupdating process can be performed iteratively for each feature. Thus itcan be determined whether an additional power management featurespresent in the table (diamond 255). If not, method 200 terminates forthat evaluation interval. If another feature is present, it can bedetermined whether a change in the feature settings has occurred sincethe last read out from the table (diamond 260). If not control passesback to diamond 255. If instead a feature change has occurred, controlpasses to diamond 270 where it can be determined whether the feature isa PCU-controlled feature. If so, one or more settings for the featurecan be updated in the PCU (block 290). Such updating can be viaconfiguration register updates or so forth. Otherwise if the updates arefor a power management feature controlled by an external agent, controlpasses to block 280 where one or more messages, e.g., write messages canbe sent to the destination agent to update the settings accordingly. Forexample, writes can be issued to target using a given message channel(e.g., QPI, integrated memory controller, a Peripheral ComponentInterconnect Express (PCI Express™ (PCIe™)) link or so forth). Althoughshown with this particular implementation in the embodiment of FIG. 3,understand the scope of the present invention is not limited in thisregard.

In one embodiment, a tuning methodology for generating topower-performance table may include the following. First, eachindividual power management feature is tuned separately while the otherfeatures are turned off. This tuning includes generating apower/performance profile across a range of workloads for each feature.As an example various benchmark workloads can be executed to generatethe profile. Second, multiple features can be enabled to a profilewhether the power/performance tradeoff met the tuning goals for overallpower/performance profile. Then individual feature tunings can beadjusted to meet overall power/performance profile goals. The abovesteps can be repeated until overall goals are reached.

By default the operating system may populate the EPB input with aprofile chosen by the end user. This tuning can be achieved via aniterative process in which different EPB values are input and workloadsrun with each setting. As the EPB input is tuned towards power savings,a user may notice a continuous degradation of response time(performance). Once a desired response time is met, the EPB value maycorrespond to a desired maximum power savings for the user's specificusage. This in essence is the goal of the tunable power performanceloadline, as each end user can tune the power/performance loadline tohis specific usage.

Embodiments can be implemented in processors for various marketsincluding server processors, desktop processors, mobile processors, andso forth. Referring now to FIG. 4, shown is a block diagram of aprocessor in accordance with an embodiment of the present invention. Asshown in FIG. 4, processor 300 may be a multicore processor including aplurality of cores 310 _(a)-310 _(n). In one embodiment, each such coremay be of an independent power domain and can be configured to operateat an independent voltage and/or frequency, and to enter turbo mode whenavailable headroom exists. The various cores may be coupled via aninterconnect 315 to a system agent or uncore 320 that includes variouscomponents. As seen, the uncore 320 may include a shared cache 330 whichmay be a last level cache. In addition, the uncore may include anintegrated memory controller 340, various interfaces 350 and a powercontrol unit 355.

In various embodiments, power control unit 355 may include a policytuning logic 359, which may be a logic to perform dynamic control ofpower management settings based on an input EPB value. As further seen,a tuning table 357 can be present to store power management featuresettings. This tuning table generated, e.g., during design of theprocessor, based on benchmark workload testing on the processor may beused to determine appropriate settings for the different powermanagement policies that map to EPB values or bins.

With further reference to FIG. 4, processor 300 may communicate with asystem memory 360, e.g., via a memory bus. In addition, by interfaces350, connection can be made to various off-chip components such asperipheral devices, mass storage and so forth. While shown with thisparticular implementation in the embodiment of FIG. 4, the scope of thepresent invention is not limited in this regard.

Referring now to FIG. 5, shown is a block diagram of a multi-domainprocessor in accordance with another embodiment of the presentinvention. As shown in the embodiment of FIG. 5, processor 400 includesmultiple domains. Specifically, a core domain 410 can include aplurality of cores 410 ₀-410 n, a graphics domain 420 can include one ormore graphics engines, and a system agent domain 450 may further bepresent. In various embodiments, system agent domain 450 may execute ata fixed frequency and may remain powered on at all times to handle powercontrol events and power management such that domains 410 and 420 can becontrolled to dynamically enter into and exit low power states. Each ofdomains 410 and 420 may operate at different voltage and/or power. Notethat while only shown with three domains, understand the scope of thepresent invention is not limited in this regard and additional domainscan be present in other embodiments. For example, multiple core domainsmay be present each including at least one core.

In general, each core 410 may further include low level caches inaddition to various execution units and additional processing elements.In turn, the various cores may be coupled to each other and to a sharedcache memory formed of a plurality of units of a last level cache (LLC)440 ₀-440 _(n). In various embodiments, LLC 440 may be shared amongstthe cores and the graphics engine, as well as various media processingcircuitry. As seen, a ring interconnect 430 thus couples the corestogether, and provides interconnection between the cores, graphicsdomain 420 and system agent circuitry 450. In one embodiment,interconnect 430 can be part of the core domain. However in otherembodiments the ring interconnect can be of its own domain.

As further seen, system agent domain 450 may include a displaycontroller 452 which may provide control of and an interface to anassociated display. As further seen, system agent domain 450 may includea power control unit 455 which can include a policy tuning logic 459 inaccordance with an embodiment of the present invention to dynamicallycontrol power management settings obtained from a tuning table 457 basedon one or more EPB values. In various embodiments, this logic mayexecute the algorithm described above in FIG. 3.

As further seen in FIG. 5, processor 400 can further include anintegrated memory controller (IMC) 470 that can provide for an interfaceto a system memory, such as a dynamic random access memory (DRAM).Multiple interfaces 480 ₀-480 _(n) may be present to enableinterconnection between the processor and other circuitry. For example,in one embodiment at least one direct media interface (DMI) interfacemay be provided as well as one or more Peripheral Component InterconnectExpress (PCI Express™ (PCIe™)) interfaces. Still further, to provide forcommunications between other agents such as additional processors orother circuitry, one or more interfaces in accordance with a Intel®Quick Path Interconnect (QPI) protocol may also be provided. Althoughshown at this high level in the embodiment of FIG. 5, understand thescope of the present invention is not limited in this regard.

Embodiments may be implemented in many different system types. Referringnow to FIG. 6, shown is a block diagram of a system in accordance withan embodiment of the present invention. As shown in FIG. 6,multiprocessor system 500 is a point-to-point interconnect system, andincludes a first processor 570 and a second processor 580 coupled via apoint-to-point interconnect 550. As shown in FIG. 6, each of processors570 and 580 may be multicore processors, including first and secondprocessor cores (i.e., processor cores 574 a and 574 b and processorcores 584 a and 584 b), although potentially many more cores may bepresent in the processors. Each of the processors can include a PCU orother logic to perform dynamic control of power management settingsbased on a resolved power management policy, as described herein.

Still referring to FIG. 6, first processor 570 further includes a memorycontroller hub (MCH) 572 and point-to-point (P-P) interfaces 576 and578. Similarly, second processor 580 includes a MCH 582 and P-Pinterfaces 586 and 588. As shown in FIG. 6, MCH's 572 and 582 couple theprocessors to respective memories, namely a memory 532 and a memory 534,which may be portions of system memory (e.g., DRAM) locally attached tothe respective processors. First processor 570 and second processor 580may be coupled to a chipset 590 via P-P interconnects 552 and 554,respectively. As shown in FIG. 6, chipset 590 includes P-P interfaces594 and 598.

Furthermore, chipset 590 includes an interface 592 to couple chipset 590with a high performance graphics engine 538, by a P-P interconnect 539.In turn, chipset 590 may be coupled to a first bus 516 via an interface596. As shown in FIG. 6, various input/output (I/O) devices 514 may becoupled to first bus 516, along with a bus bridge 518 which couplesfirst bus 516 to a second bus 520. Various devices may be coupled tosecond bus 520 including, for example, a keyboard/mouse 522,communication devices 526 and a data storage unit 528 such as a diskdrive or other mass storage device which may include code 530, in oneembodiment. Further, an audio I/O 524 may be coupled to second bus 520.Embodiments can be incorporated into other types of systems includingmobile devices such as a smart cellular telephone, tablet computer,netbook, ultrabook, or so forth.

FIG. 7 is a block diagram of a system 600 coupled with point-to-point(PtP) system interconnects in accordance with a given cache coherenceprotocol using QPI links as the system interconnect. In the embodimentshown, each processor 610 is coupled to two PtP links 625 and includesone instance of an integrated memory controller 615 that in turn iscoupled to a corresponding local portion of a system memory 620. Eachprocessor can perform power management techniques using optimizedsettings obtained from a tuning table in accordance with an embodimentof the present invention. The processors are connected to aninput/output hub (IOH) 630 using one link and the remaining link is usedto connect the two processors.

Referring now to FIG. 8, shown is a block diagram of a system inaccordance with another embodiment of the present invention. As shown inFIG. 8, system 700 may be a partially connected quad processor system inwhich each processor 710 (each of which may be multicore multi-domainprocessors) is coupled to each other processor via a PtP link and iscoupled to a local portion of memory (e.g., dynamic random access memory(DRAM)) 720 via a memory interconnect coupled to an integrated memorycontroller 715 of the corresponding processor. In the partiallyconnected system of FIG. 8, note the presence of two IOHs 730 and 740such that processors 710 ₀ and 710 ₁ are directly coupled to IOH 730 andsimilarly processors 710 ₂ and 710 ₃ are directly coupled to IOH 740.

Embodiments may be implemented in code and may be stored on anon-transitory storage medium having stored thereon instructions whichcan be used to program a system to perform the instructions. The storagemedium may include, but is not limited to, any type of disk includingfloppy disks, optical disks, solid state drives (SSDs), compact diskread-only memories (CD-ROMs), compact disk rewritables (CD-RWs), andmagneto-optical disks, semiconductor devices such as read-only memories(ROMs), random access memories (RAMs) such as dynamic random accessmemories (DRAMs), static random access memories (SRAMs), erasableprogrammable read-only memories (EPROMs), flash memories, electricallyerasable programmable read-only memories (EEPROMs), magnetic or opticalcards, or any other type of media suitable for storing electronicinstructions.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A processor comprising: at least one computingelement and a power controller to control a plurality of powermanagement features of the processor, the power controller to receive anenergy performance bias (EPB) value corresponding to a single inputvalue to control the plurality of power management features, the EPBvalue to be provided by an external entity, the power controller toupdate at least one setting of at least one of the plurality of powermanagement features based on the EPB value, wherein the power controllerincludes a tuning circuit to update the at least one setting of the atleast one power management feature responsive to the EPB value, thetuning circuit including a sampler to receive an EPB value from aplurality of threads and a combiner to generate a global EPB value fromthe EPB value from the plurality of threads.
 2. The processor of claim1, wherein the power controller is to access a table based at least inpart on the EPB value, and to use information from the table to updatethe at least one setting.
 3. The processor of claim 1, wherein the powercontroller is to generate a bin value from the global EPB value and toaccess the table using the bin value.
 4. The processor of claim 1,wherein the tuning circuit is to update at least one setting of a firstpower management feature controlled by the power controller, and to senda message to an interconnect that couples the processor to a secondcomponent of a system to update at least one setting of a second powermanagement feature controlled by the interconnect.
 5. The processor ofclaim 2, wherein the table includes a plurality of entries each having aplurality of fields each associated with a range of the EPB value andincluding a setting for a power management feature.
 6. The processor ofclaim 5, wherein the table includes a first set of entries associatedwith the plurality of power management features and further accessed bya workload configuration value for a first workload type and a secondset of entries associated with the plurality of power managementfeatures and further accessed by a workload configuration value for asecond workload type.
 7. A method comprising: receiving an energyperformance bias (EPB) value, in a power controller of a processor of asystem, from a plurality of threads executing on the processor, the EPBvalue to indicate a preference of a user for a tradeoff between poweroptimization and performance optimization; determining a global EPBvalue from the received EPB value of the plurality of threads;accessing, by the power controller, a power-performance table based onthe EPB value; and updating at least one setting of a power managementfeature controlled by the power controller based on information obtainedfrom the power-performance table.
 8. The method of claim 7, furthercomprising selecting a bin of a plurality of bins, each associated witha power-performance profile using the global EPB value.
 9. The method ofclaim 8, wherein accessing the power-performance table based on the EPBvalue includes accessing the power-performance table using the selectedbin, and updating at least one setting of a first power managementfeature controlled by the power controller, the at least one settingobtained from a field of an entry of the power-performance tableassociated with the selected bin.
 10. The method of claim 9, furthercomprising sending a message to a target agent coupled to the processor,the message including at least one updated setting for a second powermanagement feature controlled by the target agent, the at least onesetting obtained from a field of an entry of the power-performance tableassociated with the selected bin.
 11. The method of claim 7, furthercomprising providing an interface to enable a user, an operating systemor a baseboard management controller to set the EPB value, andcontrolling a plurality of power management features via input of theEPB value.
 12. The method of claim 7, further comprising receiving theEPB value with a first value for a first portion of a day and with asecond value for a second portion of the day, wherein the first value isto configure the system for high performance during the first portion ofthe day corresponding to peak user hours, and the second value toconfigure the system for higher power savings during the second portionof the day corresponding to non-peak user hours.
 13. The method of claim7, further comprising receiving a plurality of EPB values during atuning process and iteratively updating at least some power managementfeature settings for each of the plurality of EPB values, whereinresponsive to performance of the system with the updated powermanagement features, a user selects a desired one of the EPB values. 14.A system comprising: a multicore processor including a plurality ofcores and a tuning circuit to dynamically select a balance between apower consumption level and a performance level based on an energyperformance bias (EPB) value, wherein the tuning circuit is to access anentry of a tuning table based at least in part on the EPB value and aworkload configuration value and to update a setting for a powermanagement feature responsive to a value stored in a field of the entryassociated with the EPB value, the workload configuration value toindicate a predominant workload type to be executed on the system, andwherein the tuning table includes a first set of entries associated witha first workload type and a second set of entries associated with asecond workload type; and a dynamic random access memory (DRAM) coupledto the processor via a memory interconnect.
 15. The system of claim 14,wherein tuning circuit is to update at least one setting of a firstpower management feature controlled by a power controller of themulticore processor, the at least one setting obtained from a field ofan entry of the tuning table associated with a bin in which the EPBvalue is included.
 16. The system of claim 15, wherein the tuningcircuit is to send a message to the memory interconnect, the messageincluding at least one updated setting for a second power managementfeature controlled by the memory interconnect, the at least one settingobtained from a field of an entry of the tuning table associated withthe bin.